On the voicecoder mailing list, Quintijn has released an installer that works on Vista. The speech wiki that was used before seems to have been spammed into oblivion, and that installer failed on vista anyways.
I also hit a few snags so here is the steps that worked for me:
Click and save the “pythonfornatlink” link. Extract the files from the download and run each one by right clicking and hitting “run as administrator.”
Click and save the “natlink” link (it contains vocola)
Run this file as administrator.
After everything’s installed, go to start -> all programs -> natlink -> Configure Natlink Gui
Got to the configure tab, enable natlink.
uncheck the box that says “Vocola uses simpscrp”
Go ahead and close the gui and you should be good to go (I rebooted at this point, but restarting dragon is probably good enough.)